Geoenvironmental aspects of mine methane emissions

Abstract

The purpose of the work is to reveal the regularities of the influence of the gaseous phase on the process of filtering carbonated liquid and to characterize the physi-cochemical processes during the implementation of the method of reducing mine methane emissions. The development of minerals can be accompanied by the release of a large amount of methane into the mined-out space. This leads to atmospheric air pollution and consequently to ecological disturbances. This causes methane emissions to the mined-out space and to the surface of the earth cause by the filtration processes of gases and liquids in the rocks. The intensity of fluid filtration through crack and pore systems depends on the content and properties of the fluids and the reservoir properties of the rocks. It is known that methane release to the atmosphere can be observed after mines have been mothballed. This is a problem for many countries around the world where coal and oil and gas fields are being exploited. Investment in methane production and utilization projects is therefore important. Research on fluids filtration processes allow for the development of effective methane recovery methods, and ways to reduce methane emission speed. The result is the reduced air pollution and an improved environmental situation. The paper presents the filtration properties of rocks with different structures and textures. Filtration of carbonated liquid (water-methane) in fractures and pores is considered. It found that an increase in methane concentration in the carbonated liquid leads to a decrease in the phase permeability coefficient for water and an increase for methane. This character of change in phase permeability leads to methane accumulation in crack and pores. The dependence of the average carbonated liquid filtration rate in a rectilinear fracture on the methane concentration and the fracture axis angle of inclination is obtained. The average ascending filtration speed of the carbonated liquid is determined to be greater than the average descending filtration speed. This is due to the effect of the ejection force that acts on the gas bubbles in the liquid. The authors propose a method of blocking methane seepage by physicochemical treatment of the rock mass. The methane blocking effect is achieved by creating a gas-tight zone in areas with a high risk of methane migration to the ground surface. The result is a reduction in methane emissions to the mined-out space and the environment. When the method is realized, the solid product of the polymer solution enters cracks with a disclosure greater than 6 μm or pore channels with an average diameter of 6 μm. At the same time, the water released by the destabi- lization of the polymer solution blocks the methane in small cracks and pores. In pore channels with an average diameter of less than 25 μm, there is a sharp increase in the dynamic viscosity of the polymer solution. This effect is due to an increase in the intermolecular interaction forces between the polymer solution and the walls of the filtration channels. Coagulation and destabilization of the polymer solution in cracks and pores is due to the separation of large agglomerates of macromolecules.